Interferometric Synthetic Aperture Radar (InSAR) is the most effective method that is capable of observing ground surface displacement in the line-of-sight (LOS) direction of a satellite antenna in an area of tens of kilometers. InSAR started to be used in earnest by observing displacement in the Landers earthquake in U.S.A. in the early 1990s, and has been advanced by the institutes of European countries. In Korea, research into the utilization of InSAR in the development of technology and the field of earth science has been conducted chiefly by the research teams of universities.
The early InSAR was used to observe sporadic ground surface displacement, attributable to large-scale geotectonic movement, i.e., an earthquake or volcanic eruptions, occurring during a period in which two images were acquired from a single interferometric pair, but has been developed into research into the observation of mean displacement velocity for multiple periods and time series analysis by the accumulation of imaging radar data over a long period. This multi-temporal observation method has improved the precision of the measurement of ground surface displacement in the LOS direction of a sensor by reducing noise phase components in images.
Recently, in order to overcome the greatest disadvantage of the conventional InSAR, i.e., the disadvantage of being able to measure only displacement in the LOS direction of an antenna, technologies for observing ground surface displacement in an along-track direction have been developed. In this regard, there is a conventional measurement method using a correlation coefficient between two images. However, this method has a limitation in terms of application in connection with an application area and the magnitude of displacement because the precision of ground surface displacement in an along-track direction measured using the method is very low.
A recently developed MAI measurement scheme has been proposed based on the split beam InSAR, and has improved precision to a level two or more times those of the conventional measurement methods. An early MAI scheme had the problem of a distortion error resulting from a change in the perpendicular baseline of an interferometric pair. In contrast, current technology has solved this problem, and is successful in measuring ground surface displacement in an along-track direction with centimeter-level precision. Accordingly, research into the performance of the observation of three-dimensional ground surface displacement via the integrated observation of the conventional InSAR and the improved MAI scheme has been conducted.
However, the precision of MAI measurement schemes known so far has been limitedly applied to the observation of large-scale ground surface displacement ranging from tens of centimeters to a few meters, such as large-scale tectonic movement or the movement of glaciers at high speed. However, these MAI measurement schemes have a difficulty observing ground surface displacement in an area in which continuous displacement occurs on a few-centimeter per year scale. Accordingly, in order to measure small-scale ground surface displacement, there is a need for a technology for improving the precision, reached by the current technology for measuring ground surface displacement in an along-track direction, to a centimeter or higher level.
Korean Patent No. 10-1111689 entitled “Method for Three-dimensional Deformation Measurement and Apparatus Thereof” presents a method including steps of: extracting ground surface displacement in the LOS direction of a synthetic aperture radar (SAR) using the InSAR data of the synthetic aperture radar; generating MAI data using forward-looking SAR data and backward-looking SAR data, and extracting ground surface displacement in the along-track direction of the SAR using the generated MAI data; and extracting three-dimensional ground surface displacement from the ground surface displacement in the LOS direction and the ground surface displacement in the along-track direction.
This technology mentioned above is advantageous in that it can extract ground surface displacement in the LOS direction and ground surface displacement in the along-track direction using the InSAR interferogram and the MAI interferogram and accurately extract three-dimensional ground surface displacement from the ground surface displacement. However, this technology mentioned above is problematic in that it has a difficulty observing ground surface displacement in an area in which continuous displacement occurs on a few-centimeter per year scale because it cannot improve the precision of a technology for measuring ground surface displacement in the along-track direction to a centimeter or higher level.